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Atrioventricular Block



Atrioventricular (AV) block occurs due to delayed conduction of an impulse between the atria or ventricles, due to intrinsic or extrinsic causes.


  • Causes of Atrioventricular (AV) Block

  • Intrinsic

  • Idiopathic degeneration
  • Myocardial infarction
  • Congenital - congenital heart disease, neonatal lupus
  • Infiltrative disease - sarcoidosis, amyloidosis, haemochromatosis
  • Cardiac procedures - valvular surgery, correction of congenital heart disease, catheter ablation
  • Systemic lupus erythematosus
  • Myocarditis
  • Extrinsic

  • Physiologic - sleep, athletes
  • Autonomic - carotid sinus massage, carotid sinus hypersensitivity
  • Drugs - beta blockers, calcium channel blockers, digoxin, adenosine, amiodarone
  • Hyperkalaemia
  • Hypothyroidism
Physiologic and autonomic causes of AV block tend to result in first degree or Mobitz I heart block, while pathologic causes tend to result in Mobitz II, advanced second degree or complete heart block.


  • ECG Findings

  • 1st degree - prolonged PR interval >200ms (5mm)
  • 2nd degree: type I Mobitz (Wenckebach) - initial normal PR interval with progressive prolongation of PR interval followed by a dropped QRS complex.
  • 2nd degree: type II Mobitz - constant PR interval with intermittently dropped QRS complexes
  • 2nd degree: advanced - two or more consecutive P waves without QRS complexes; may be in a 3:1, 4:1 or higher pattern
  • 3rd degree - complete dissociation of P waves and QRS complexes
  • Examples

  • 1st degree AV block
  • 1st degree AV block
  • 2nd degree AV block: type I Mobitz
  • 2nd degree AV block type I Mobitz
  • 2nd degree AV block: type II Mobitz
  • 2nd degree AV block type II Mobitz
  • Advanced 2nd degree AV block
  • Advanced 2nd degree AV block
  • 3rd degree AV block
  • 3rd degree AV block
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